| Abstrakt: |
Derivation of formulæ to compute direct and induced stresses developed in wire ropes by static or moving tension, bending, and horizontally suspended loads. The values for the bending stresses produced in ropes that are passed over sheaves, as determined by the formulæ of Reuleaux, Rankine, Unwin and Hewitt are correct only for ropes composed of straight wires. Owing to the twisting of the wires in the formation of modern rope, the actual bending stress in it is much smaller than in a solid bar, and its true value, S, may be computed by replacing in the fundamental assumptions the modulus of elasticity of a solid bar, with ER, the experimental value or the modulus of elasticity of the rope as a whole; thus the Reuleaux formula becomes S = ER (d/D) where d is the diameter of the wire in the rope, and D the diameter of the bend. The author develops a method for determining the moduli of elasticity of both strands and rope in cases where experimental data are not available. In regard to the customary practice followed in specifications, general remarks are offered on the required proportionality between the sheave diameters and the size of the rope, the manner of classifying strengths in the manufacturer’s rope catalog, and the special requirements in the physical properties of the wire forming the rope. |
